Stripline detector for in situ battery and fuel cell NMR

ABSTRACT

Provided are batteries and fuel cells incorporating a stripline detector for use in nuclear magnetic resonance (NMR). The stripline batteries and fuel cells can be used for in situ NMR measurement of battery or fuel cell chemistry. Also provided are methods for measuring in situ battery and fuel cell NMR using the stripline batteries and fuel cells of the invention.

RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.15/682,075, filed Aug. 21, 2017, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/377,906, filed Aug. 22, 2016,the entire disclosures of which are hereby incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under grant numberFG02-07ER15895 awarded by the Department of Energy. The government hascertain rights in the invention.

BACKGROUND

Nuclear magnetic resonance (NMR) is a well-established spectroscopictechnique for the identification of chemical species and is broadlyapplied in many different fields like synthetic and supramolecularchemistry, catalysis, materials science, biology, and medicine. In asimple NMR experiment, the sample is exposed to a static magnetic field(B₀). After excitation of the nuclear spin system using a short radiofrequency (rf) pulse, the processing magnetization is detected. Therecorded resonance frequencies (peaks in the NMR spectra) are a probe ofthe local electronic environment of a specific nucleus in a molecule.Additionally, fine structure like J-couplings and dipolar couplings area measure of chemical bonding and distance between two nuclei,respectively. NMR is a non-invasive technique and provides directquantitative information.

NMR has been used to study batteries, albeit with limited success. Intraditional battery NMR, the battery under investigation is placedinside a solenoid coil. The metal battery electrodes, essential to thebattery operation, are necessarily also placed inside the coil, whichlowers the sensitivity and resolution of the resulting data. In the caseof electrodes that are thick compared to the rf skin depth at the NMRfrequency, in situ NMR may actually be impossible. In that case, the rffield is effectively screened by the metal electrodes and is preventedfrom imparting the magnetic energy necessary for NMR to the interior ofthe battery.

Stripline detectors have been demonstrated in the past for limited NMRapplications involving experiments where sample volumes are extremelylimited. In such experiments, the stripline detector has the advantageof high theoretical signal-to-noise while minimizing the magneticsusceptibility challenges that plague traditional microcoil solenoidNMR. Van Bentum et al., J Magn Reson 189(1): 104-13 (2007); Bart et al.,J Am Chem Soc 131(14): 5014-5 (2009); Bart et al., J Magn Reson 201(2):175-85 (2009); U.S. Patent Application Publication 2008/0290869 toHutton et al.; and U.S. Patent Application Publication 2015/0008917 toKentgens et al., the entire contents of which are incorporated herein byreference.

SUMMARY OF THE INVENTION

Provided are battery and fuel cell systems featuring an internalstripline detector. The essentially 2-dimensional stripline detector isbuilt into the battery or fuel cell itself during fabrication, andallows high quality NMR data to be obtained in situ during battery orfuel cell operation regardless of the thickness of the electrodes. Thedevice can be used to study any NMR active nucleus of interest and so isextremely versatile in studying a variety of battery and fuel celltypes. This device thus has the potential to allow investigation of manypoorly understood battery and fuel cell chemistries, and provides themeans to monitor the creation and consumption of chemical species duringactual battery or fuel cell operation conditions.

An aspect of the invention is a battery comprising a stripline detector.

In certain embodiments, the battery further comprises metallic cathodeand anode support plates arranged in substantially parallel planes andsituated on opposite sides of the stripline detector.

In certain embodiments, the metallic cathode support plate comprisesaluminum.

In certain embodiments, the metallic cathode support plate furthercomprises a cathode material deposited on the cathode support plate.

In certain embodiments, the cathode material deposited on the cathodesupport plate is selected from the group consisting of lithium ironphosphate (LiFePO₄), lithium cobalt oxide (LiCoO₂), and spinel cathodematerials.

In certain embodiments, the metallic anode support plate comprisescopper.

In certain embodiments, the metallic anode support plate furthercomprises an anode material deposited on the anode support plate.

In certain embodiments, the anode material deposited on the anodesupport plate is graphite.

In certain embodiments, the battery further comprises a firstnonconductive separator situated between the stripline detector and themetallic cathode support plate, and a second nonconductive separatorsituated between the stripline detector and the metallic anode supportplate, wherein the first nonconductive separator electrically isolatesthe stripline detector from the cathode, and the second nonconductiveseparator electrically isolates the stripline detector from the anode.

In certain embodiments, the first nonconductive separator and the secondnonconductive separator independently comprise a material selected fromthe group consisting of polyethylene, polypropylene, andpolytetrafluoroethylene (PTFE).

In certain embodiments, the first nonconductive separator and the secondnonconductive separator are the same.

In certain embodiments, the first nonconductive separator and the secondnonconductive separator are a single nonconductive separator.

An aspect of the invention is a fuel cell comprising a striplinedetector.

In certain embodiments, the fuel cell further comprises metallic cathodeand anode support plates arranged in substantially parallel planes andsituated on opposite sides of the stripline detector.

In certain embodiments, the metallic cathode support plate comprisesaluminum.

In certain embodiments, the metallic cathode support plate furthercomprises a cathode material deposited on the cathode support plate.

In certain embodiments, the cathode material deposited on the cathodesupport plate is selected from the group consisting of lithium ironphosphate (LiFePO₄), lithium cobalt oxide (LiCoO₂), and spinel cathodematerials.

In certain embodiments, the metallic anode support plate comprisescopper.

In certain embodiments, the metallic anode support plate furthercomprises an anode material deposited on the anode support plate.

In certain embodiments, the anode material deposited on the anodesupport plate is graphite.

In certain embodiments, the fuel cell further comprises a firstnonconductive separator situated between the stripline detector and themetallic cathode support plate, and a second nonconductive separatorsituated between the stripline detector and the metallic anode supportplate, wherein the first nonconductive separator electrically isolatesthe stripline detector from the cathode, and the second nonconductiveseparator electrically isolates the stripline detector from the anode.

In certain embodiments, the first nonconductive separator and the secondnonconductive separator independently comprise a material selected fromthe group consisting of polyethylene, polypropylene, andpolytetrafluoroethylene (PTFE).

In certain embodiments, the first nonconductive separator and the secondnonconductive separator are the same.

In certain embodiments, the first nonconductive separator and the secondnonconductive separator are a single nonconductive separator.

An aspect of the invention is a method for measuring in situ batterynuclear magnetic resonance (NMR), comprising

providing a stripline battery of the invention;

connecting the stripline detector to an NMR circuit;

isolating electrode leads of the battery from alternating current NMRcircuitry; and

cycling the battery while acquiring NMR data from the battery.

An aspect of the invention is a method for measuring in situ fuel cellnuclear magnetic resonance (NMR), comprising

providing a stripline fuel cell of the invention;

connecting the stripline detector to an NMR circuit;

isolating electrode leads of the battery from alternating current NMRcircuitry; and

cycling the fuel cell while acquiring NMR data from the fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic drawing depicting a front view of striplinedetector geometry. The narrow neck is of length l and of width w.

FIG. 1B is a schematic drawing depicting side view stripline detectorgeometry together with radiofrequency (rf) homogenizing ground plates.Dimension d represents the distance between the two plates. Thesensitive region is above and below the narrow neck of the striplinedetector.

FIG. 2 is a schematic drawing depicting stripline battery assembly. A:stripline detector; B: aluminized battery pouch; C: separator material;D: copper plate acting as anode support and rf homogenizing plate; E:aluminum plate acting as cathode support and rf homogenizing plate. Inthe final assembly, the ends of the stripline detector and the tabs ofthe cathode and anode support plates protrude through the pouch seal forelectrical connection.

FIG. 3 is a circuit diagram depicting electrical connections to astripline battery cell. C_(F), filter capacitor; C_(LP), low passcapacitor; C_(M), variable impedance matching capacitor; C_(T), tuningcapacitor; R, resistor; RF, radio frequency pulse; WE, batterypotentiostat working electrode.

FIG. 4 is a graph depicting ⁷Li in situ NMR spectra for a lithium ironphosphate (LiFePO₄) vs. graphite pouch cell with stripline operatingwith 0.1 mA charge/discharge current.

FIG. 5 is a graph depicting ⁷Li in situ NMR spectra for a lithium ironphosphate (LiFePO₄) vs. graphite pouch cell with stripline. Depicted arefully charged peak (red dotted trace), initial fully discharged peak(black solid trace), and final fully discharged peak (blue solid trace).

DETAILED DESCRIPTION

A stripline detector is a thin strip of metal or wire. For use in NMR,the metallic strip or wire is confined between two metal shieldingplates. To obtain a high rf-field strength, which is necessary for highsensitivity, the strip is constricted in an hourglass shape. In thenarrowed (neck) area of the constriction, the current density increaseslocally, and with that the rf-field strength. Alternatively, in the caseof a wire, the current density likewise increases locally, and with thatthe rf-field strength.

In an embodiment, the solenoid detector itself consists of a thinmetallic strip cut into an hourglass shape (see FIG. 1A). Theconstriction in the center marks the sensitive region of the detectorwhere the narrowed body provides for high current densities. Currentflowing through the neck of the stripline produces a circulatingmagnetic field that circles the stripline much like the magnetic fieldproduced by current flowing in a wire. This magnetic field strengthdecreases as 1/r, where r is the distance normal to the stripline. Thisproperty is what makes striplines (and wires) poor NMR “coils”, as it isimpossible to provide a homogeneous magnetic field to a sample underthese conditions. However, it has been shown by Kentgens, et al. thatplacing ground plates above and below the stripline detector at anoptimal distance distorts the electromagnetic field produced by the wireinto a region of homogeneous magnetic field above and below thestripline. Van Bentum et al., J Magn Reson 189(1): 104-13 (2007). Thisconfiguration makes it possible to create the homogenous fields oversmall regions necessary to measure tiny quantities (nL) of scarcesamples, which would be a challenge for the traditional NMR detectionscheme.

The present system uses the stripline coil in a completely new way. Thepresent inventors discovered, unexpectedly, that the so-called groundplates, which are necessary to maintain the homogeneous rf field in thesample region, do not need to be held at ground potential with respectto the NMR ground potential. Holding the plates at different potentialsto one another does not affect the NMR data, provided sufficientelectronic filtering is used for rf isolation. This leads to the idea ofusing the ground plates as battery or fuel cell electrodes.

An aspect of the invention is a battery comprising a stripline detector.The stripline detector can be incorporated into any type of battery,e.g., lithium-ion batteries, including without limitation lithium cobaltoxide (LiCoO₂), lithium iron phosphate (LiFePO₄), lithium manganeseoxide (LiMn₂O₄; Li₂MnO₃), lithium nickel manganese cobalt oxide(LiNiMnCoO₂), lithium nickel cobalt aluminum oxide (LiNiCoAlO₂), lithiumtitanate (Li₄T₁₅O₁₂), and lithium sulfur batteries.

Referring to FIG. 1A, the stripline detector is cut from a thin (e.g.,35 micron thick) conductive metal (e.g., copper, aluminum, or gold)sheet and can be made in any physical dimensions appropriate for thebattery or fuel cell under investigation. The narrowed neck section isof length l and width w. For optimum performance, l/w should beapproximately 5.

In certain embodiments, the stripline detector is cut from a thin (e.g.,35 micron thick) graphene sheet and can be made in any physicaldimensions appropriate for the battery or fuel cell under investigation.For optimum performance, l/w should be approximately 5.

In certain embodiments, the stripline can be a thin layer of aconducting metal, such as copper, aluminum, or gold, that is depositedonto a nonconductive substrate such as mica. For optimal performance,the metal will be constructed and arranged to have a narrow or narrowedsection with l/w approximately 5.

In certain embodiments, the stripline can be a thin layer of graphenedeposited on a nonconductive substrate such as mica. For optimalperformance, the graphene will be constructed and arranged to have anarrow or narrowed section with l/w approximately 5.

In certain embodiments, the battery further comprises metallic cathodeand anode support plates arranged in substantially parallel planes andsituated on opposite sides of the stripline detector. The metallicsupport plates can take any 2-dimensional shape, including, for example,rectangular, square, circular, oval, and the like, provided that the twoplates can cover, i.e., span, the full length (l) and width (w) of atleast the neck or narrowed part of the stripline. In certainembodiments, the metallic support plates are annular in configuration,i.e., a central portion is absent. In certain embodiments, the metalliccathode and anode support plates are similar to each other in size andshape. In certain embodiments, the metallic cathode and anode supportplates are substantially identical to each other in size and shape. Incertain embodiments, the metallic cathode and anode support plates aresubstantially identical to each other in size and shape, and they aresimilarly disposed about the stripline, one over the other.

In certain embodiments, the metallic cathode and anode support platesare substantially identical annular rectangles, and they are similarlydisposed about the stripline, one over the other.

In certain embodiments, the metallic cathode and anode support platesare substantially identical annular squares, and they are similarlydisposed about the stripline, one over the other.

Referring to FIG. 1B, the system of the invention incorporates thestripline detector inside a working battery or fuel cell, with themetallic cathode and anode support plates acting as the rf homogenizingplates. For optimum performance, w/d should be approximately 1.

In certain embodiments, the metallic cathode support plate comprisesaluminum.

In certain embodiments, the metallic cathode support plate consistsessentially of aluminum.

In certain embodiments, the metallic cathode support plate consists ofaluminum.

In certain embodiments, the metallic anode support plate comprisescopper.

In certain embodiments, the metallic anode support plate consistsessentially of copper.

In certain embodiments, the metallic anode support plate consists ofcopper.

In certain embodiments, the metallic cathode support plate furthercomprises a cathode material deposited on the cathode support plate. Thecathode material can be deposited on the cathode support plate using anysuitable method.

In certain embodiments, the cathode material deposited on the cathodesupport plate is selected from the group consisting of lithium ironphosphate (LiFePO₄), lithium cobalt oxide (LiCoO₂), and spinel cathodematerials.

In certain embodiments, the cathode material deposited on the cathodesupport plate comprises LiFePO₄.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists essentially of LiFePO₄.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists of LiFePO₄.

In certain embodiments, the cathode material deposited on the cathodesupport plate comprises LiCoO₂.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists essentially of LiCoO₂.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists of LiCoO₂.

In certain embodiments, the cathode material deposited on the cathodesupport plate comprises a spinel cathode material.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists essentially of a spinel cathode material.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists of a spinel cathode material.

Spinels are well known in the art, and nonlimiting examples of spinelsinclude those of general formula LiM_(x)Mn_(2-x)O₄, wherein M representsmetal ion. In certain embodiments, spinels include those of generalformula LiNi_(x)Mn_(2-x)O₄, e.g., LiNi_(0.5)Mn_(1.5)O₄.

In accordance with each of the foregoing, in certain embodiments themetallic anode support plate further comprises an anode materialdeposited on the anode support plate. The anode material can bedeposited on the anode support plate using any suitable method.

In certain embodiments, the anode material deposited on the anodesupport plate comprises graphite.

In certain embodiments, the anode material deposited on the anodesupport plate consists essentially of graphite.

In certain embodiments, the anode material deposited on the anodesupport plate consists of graphite.

The cathode and anode materials, as well as the electrolyte and allproducts and reactants of the battery chemistry, are thus in thesensitive region of the stripline detector (above the narrowed neck oflength l. In this scheme, the electrodes, rather than being a hindranceto high-resolution NMR detection, are actually essential to the designby acting to homogenize the if field in the detection region. Moreover,the presence of the stripline does not compromise or hinder theperformance of the battery itself; the cathode and anode are designed sothat much of their surface areas overlap the stripline neck, and thussignificant ion transport is conducted through the electrolyte withoutencountering the stripline. This setup is therefore ideal for measuringin situ battery NMR, as high-resolution NMR data can be acquired quicklywhile the battery is cycled without disturbing the system in any way toeffect the measurement.

Referring to FIG. 2, in accordance with each of the precedingembodiments, in certain embodiments the battery further comprises afirst nonconductive separator situated between the stripline detectorand the metallic cathode support plate, and a second nonconductiveseparator situated between the stripline detector and the metallic anodesupport plate, wherein the first nonconductive separator electricallyisolates the stripline detector from the cathode, and the secondnonconductive separator electrically isolates the stripline detectorfrom the anode.

In certain embodiments, the first nonconductive separator comprisespolyethylene.

In certain embodiments, the first nonconductive separator consistsessentially of polyethylene.

In certain embodiments, the first nonconductive separator consists ofpolyethylene.

In certain embodiments, the first nonconductive separator comprisespolypropylene.

In certain embodiments, the first nonconductive separator consistsessentially of polypropylene.

In certain embodiments, the first nonconductive separator consists ofpolypropylene.

In certain embodiments, the first nonconductive separator comprisespolytetrafluoroethylene (PTFE).

In certain embodiments, the first nonconductive separator consistsessentially of PTFE.

In certain embodiments, the first nonconductive separator consists ofPTFE.

In certain embodiments, the second nonconductive separator comprisespolyethylene.

In certain embodiments, the second nonconductive separator consistsessentially of polyethylene.

In certain embodiments, the second nonconductive separator consists ofpolyethylene.

In certain embodiments, the second nonconductive separator comprisespolypropylene.

In certain embodiments, the second nonconductive separator consistsessentially of polypropylene.

In certain embodiments, the second nonconductive separator consists ofpolypropylene.

In certain embodiments, the second nonconductive separator comprisesPTFE.

In certain embodiments, the second nonconductive separator consistsessentially of PTFE.

In certain embodiments, the second nonconductive separator consists ofPTFE.

In certain embodiments, the first nonconductive separator and the secondnonconductive separator are the same. For example, in certainembodiments, first nonconductive separator consists of polyethylene, andsecond nonconductive separator also consists of polyethylene. As anotherexample, in certain embodiments, first nonconductive separator consistsof polypropylene, and second nonconductive separator also consists ofpolypropylene. As yet another example, in certain embodiments, firstnonconductive separator consists of PTFE, and second nonconductiveseparator also consists of PTFE.

In accordance with each of the foregoing embodiments, in certainembodiments, the first nonconductive separator and the secondnonconductive separator are a single nonconductive separator. Forexample, the first nonconductive separator and the second nonconductiveseparator are constructed and arranged as a single sheet of materialthat may be folded over or otherwise reflected onto itself so as tocover or envelop the stripline detector, thereby electrically isolatingthe stripline detector from the cathode and the anode.

The in situ NMR battery is assembled as shown in FIG. 2. The cathodematerial is deposited on an aluminum substrate. The anode material isdeposited on a copper substrate. These electrodes then act as therf-homogenizing plates for the NMR as well as battery electrodes for theelectrochemistry. A stripline inductor is fashioned from a 35 micrometerthick copper sheet with dimensions as shown in FIG. 1A. A separatormaterial is placed on either side of the stripline to isolate itelectrically from the cathode and anode. A flexible pouch cell isassembled in an inert atmosphere in a glovebox and partially sealed. Inthe glovebox, before the final edge is sealed, ˜1 mL of electrolyte isadded to the pouch, flooding the electrodes and wetting the separator.The copper stripline and battery electrode leads extend outside thesealed pouch for electrical connection; the seal is airtight around themetal protrusions. The battery is then cycled several times to ensurestability and charging capability.

FIG. 3 shows an electrical schematic for the in situ NMR probe. Thebattery electrode leads protruding from the side are isolated from thealternating current (ac) NMR circuitry by low pass filters consisting ofa series combination of resistors R and capacitors C_(LP). The batterypotentiostat working electrode WE connects to the aluminum (cathode)plate. The potentiostat auxiliary and reference electrode leads connectto the copper (anode) plate. This effectively shunts to ground any accurrents induced in the electrode lines by the adjacent high power acNMR circuitry, while allowing the passage of the direct current (dc)currents necessary for charging and discharging of the battery. The NMRcircuit itself is a traditional parallel oscillating tank circuit with avariable tuning capacitor C_(T) in parallel with the stripline detector.A variable impedance matching capacitor C_(M) taps the rf pulse into thetank circuit. An additional two capacitors C_(F) on the input and outputof the stripline act as filters that pass the high frequency rf currentsbut effectively block any low frequency currents from the potentiostatthat may couple into the NMR circuit. The stripline detector replacesthe traditional solenoid inductor in this circuit.

An aspect of the invention is a fuel cell comprising a striplinedetector. The stripline detector can be incorporated into any type offuel cell.

Referring again to FIG. 1A, in certain embodiments, the striplinedetector is cut from a thin (e.g., 35 micron thick) conductive metal(e.g., copper, aluminum, or gold) sheet and can be made in any physicaldimensions appropriate for the fuel cell under investigation. Foroptimum performance, l/w should be approximately 5.

In certain embodiments, the stripline detector is cut from a thin (e.g.,35 micron thick) graphene sheet and can be made in any physicaldimensions appropriate for the fuel cell under investigation. Foroptimum performance, l/w should be approximately 5.

In certain embodiments, the stripline can be a thin layer of aconducting metal, such as copper, aluminum, or gold, that is depositedonto a nonconductive substrate such as mica. For optimal performance,the metal will be constructed and arranged to have a narrow or narrowedsection with l/w approximately 5.

In certain embodiments, the stripline can be a thin layer of graphenedeposited on a nonconductive substrate such as mica. For optimalperformance, the graphene will be constructed and arranged to have anarrow or narrowed section with l/w approximately 5.

In certain embodiments, the fuel cell further comprises metallic cathodeand anode support plates arranged in substantially parallel planes andsituated on opposite sides of the stripline detector. The metallicsupport plates can take any 2-dimensional shape, including, for example,rectangular, square, circular, oval, and the like, provided that the twoplates can cover, i.e., span, the full length (l) and width (w) of atleast the neck or narrowed part of the stripline. In certainembodiments, the metallic support plates are annular in configuration,i.e., a central portion is absent. In certain embodiments, the metalliccathode and anode support plates are similar to each other in size andshape. In certain embodiments, the metallic cathode and anode supportplates are substantially identical to each other in size and shape. Incertain embodiments, the metallic cathode and anode support plates aresubstantially identical to each other in size and shape, and they aresimilarly disposed about the stripline and one over the other.

In certain embodiments, the metallic cathode and anode support platesare substantially identical annular rectangles, and they are similarlydisposed about the stripline and one over the other.

In certain embodiments, the metallic cathode and anode support platesare substantially identical annular squares, and they are similarlydisposed about the stripline and one over the other.

Referring again to FIG. 1B, the system of the invention incorporates thestripline detector inside a working fuel cell, with the metallic cathodeand anode support plates acting as the rf homogenizing plates. Foroptimum performance, w/d should be approximately 1.

In certain embodiments, the metallic cathode support plate comprisesaluminum.

In certain embodiments, the metallic cathode support plate consistsessentially of aluminum.

In certain embodiments, the metallic cathode support plate consists ofaluminum.

In certain embodiments, the metallic anode support plate comprisescopper.

In certain embodiments, the metallic anode support plate consistsessentially of copper.

In certain embodiments, the metallic anode support plate consists ofcopper.

In certain embodiments, the metallic cathode support plate furthercomprises a cathode material deposited on the cathode support plate. Thecathode material can be deposited on the cathode support plate using anysuitable method.

In certain embodiments, the cathode material deposited on the cathodesupport plate is selected from the group consisting of lithium ironphosphate (LiFePO₄), lithium cobalt oxide (LiCoO₂), and spinel cathodematerials.

In certain embodiments, the cathode material deposited on the cathodesupport plate comprises LiFePO₄.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists essentially of LiFePO₄.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists of LiFePO₄.

In certain embodiments, the cathode material deposited on the cathodesupport plate comprises LiCoO₂.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists essentially of LiCoO₂.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists of LiCoO₂.

In certain embodiments, the cathode material deposited on the cathodesupport plate comprises a spinel cathode material.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists essentially of a spinel cathode material.

In certain embodiments, the cathode material deposited on the cathodesupport plate consists of a spinel cathode material.

Spinels are well known in the art, and nonlimiting examples of spinelsinclude LiNi_(x)Mn_(2-x)O₄, e.g., LiNi_(0.5)Mn_(1.5)O₄.

In accordance with each of the foregoing, in certain embodiments themetallic anode support plate further comprises an anode materialdeposited on the anode support plate. The anode material can bedeposited on the anode support plate using any suitable method.

In certain embodiments, the anode material deposited on the anodesupport plate comprises graphite.

In certain embodiments, the anode material deposited on the anodesupport plate consists essentially of graphite.

In certain embodiments, the anode material deposited on the anodesupport plate consists of graphite.

The cathode and anode materials, as well as the electrolyte and allproducts and reactants of the fuel cell chemistry, are thus in thesensitive region of the stripline detector (above the narrowed neck “l”.In this scheme, the electrodes, rather than being a hindrance tohigh-resolution NMR detection, are actually essential to the design byacting to homogenize the if field in the detection region. Moreover, thepresence of the stripline does not compromise or hinder the performanceof the fuel cell itself; the cathode and anode are designed so that muchof their surface areas overlap the stripline neck, and thus significantion transport is conducted through the electrolyte without encounteringthe stripline. This setup is therefore ideal for measuring in situ fuelcell NMR, as high-resolution NMR data can be acquired quickly while thefuel cell is cycled without disturbing the system in any way to effectthe measurement.

Referring again to FIG. 2, in accordance with each of the precedingembodiments, in certain embodiments the fuel cell further comprises afirst nonconductive separator situated between the stripline detectorand the metallic cathode support plate, and a second nonconductiveseparator situated between the stripline detector and the metallic anodesupport plate, wherein the first nonconductive separator electricallyisolates the stripline detector from the cathode, and the secondnonconductive separator electrically isolates the stripline detectorfrom the anode.

In certain embodiments, the first nonconductive separator comprisespolyethylene.

In certain embodiments, the first nonconductive separator consistsessentially of polyethylene.

In certain embodiments, the first nonconductive separator consists ofpolyethylene.

In certain embodiments, the first nonconductive separator comprisespolypropylene.

In certain embodiments, the first nonconductive separator consistsessentially of polypropylene.

In certain embodiments, the first nonconductive separator consists ofpolypropylene.

In certain embodiments, the first nonconductive separator comprisesPTFE.

In certain embodiments, the first nonconductive separator consistsessentially of PTFE.

In certain embodiments, the first nonconductive separator consists ofPTFE.

In certain embodiments, the second nonconductive separator comprisespolyethylene.

In certain embodiments, the second nonconductive separator consistsessentially of polyethylene.

In certain embodiments, the second nonconductive separator consists ofpolyethylene.

In certain embodiments, the second nonconductive separator comprisespolypropylene.

In certain embodiments, the second nonconductive separator consistsessentially of polypropylene.

In certain embodiments, the second nonconductive separator consists ofpolypropylene.

In certain embodiments, the second nonconductive separator comprisesPTFE.

In certain embodiments, the second nonconductive separator consistsessentially of PTFE.

In certain embodiments, the second nonconductive separator consists ofPTFE.

In certain embodiments, the first nonconductive separator and the secondnonconductive separator are the same. For example, in certainembodiments, first nonconductive separator consists of polyethylene, andsecond nonconductive separator also consists of polyethylene. As anotherexample, in certain embodiments, first nonconductive separator consistsof polypropylene, and second nonconductive separator also consists ofpolypropylene. As yet another example, in certain embodiments, firstnonconductive separator consists of PTFE, and second nonconductiveseparator also consists of PTFE.

In accordance with each of the foregoing embodiments, in certainembodiments, the first nonconductive separator and the secondnonconductive separator are a single nonconductive separator. Forexample, the first nonconductive separator and the second nonconductiveseparator are constructed and arranged as a single sheet of materialthat may be folded over or otherwise reflected onto itself so as tocover or envelop the stripline detector, thereby electrically isolatingthe stripline detector from the cathode and the anode.

The in situ NMR fuel cell is assembled as shown in FIG. 2. The cathodematerial is deposited on an aluminum substrate. The anode material isdeposited on a copper substrate. These electrodes then act as therf-homogenizing plates for the NMR as well as fuel cell electrodes forthe electrochemistry. A stripline inductor is fashioned from a 35micrometer thick copper sheet with dimensions as shown in FIG. 1A. Aseparator material is placed on either side of the stripline to isolateit electrically from the cathode and anode. A flexible pouch cell isassembled in an inert atmosphere in a glovebox and partially sealed. Inthe glovebox, before the final edge is sealed, ˜1 mL of electrolyte isadded to the pouch, flooding the electrodes and wetting the separator.The copper stripline and fuel cell electrode leads extend outside thesealed pouch for electrical connection; the seal is airtight around themetal protrusions. The fuel cell is then cycled several times to ensurestability and charging capability.

An aspect of the invention is a method for measuring in situ batterynuclear magnetic resonance (NMR), comprising

providing a battery of the invention;

connecting the stripline detector to an NMR circuit;

isolating electrode leads of the battery from alternating current NMRcircuitry; and

cycling the battery while acquiring NMR data from the battery.

For example, in an embodiment, the method comprises:

providing an apparatus having (i) a magnetic field generating apparatuslocated in a cryostat and surrounding a bore defining an NMR workingregion; (ii) a system for performing an NMR process on a battery of theinvention in the NMR working region; and (iii) optionally a batterypositioning mechanism which can be inserted into the bore to bring thebattery into the NMR working region, the magnetic field generatingapparatus being suitably structured so that the magnetic field in theNMR working region has a homogeneity or profile suitable for performingan NMR process on the battery, wherein the magnetic field generatingapparatus comprises a magnet assembly located in the cryostat andsurrounding the NMR working area bore so as to define the NMR workingregion in the bore, wherein the magnet assembly is suitably shielded sothat the magnetic field in the NMR working region has a homogeneity orprofile suitable for performing an NMR measurement on the battery;

preparing the battery for the NMR process;

optionally using the battery positioning mechanism to insert the batteryinto the NMR working region; and

performing an NMR measurement on the battery.

An aspect of the invention is a method for measuring in situ fuel cellnuclear magnetic resonance (NMR), comprising

providing a fuel cell of the invention;

connecting the stripline detector to an NMR circuit;

isolating electrode leads of the fuel cell from alternating current NMRcircuitry; and

cycling the fuel cell while acquiring NMR data from the fuel cell.

For example, in an embodiment, the method comprises:

providing an apparatus having (i) a magnetic field generating apparatuslocated in a cryostat and surrounding a bore defining an NMR workingregion; (ii) a system for performing an NMR process on a fuel cell ofthe invention in the NMR working region; and (iii) optionally a fuelcell positioning mechanism which can be inserted into the bore to bringthe fuel cell into the NMR working region, the magnetic field generatingapparatus being suitably structured so that the magnetic field in theNMR working region has a homogeneity or profile suitable for performingan NMR process on the fuel cell, wherein the magnetic field generatingapparatus comprises a magnet assembly located in the cryostat andsurrounding the NMR working area bore so as to define the NMR workingregion in the bore, wherein the magnet assembly is suitably shielded sothat the magnetic field in the NMR working region has a homogeneity orprofile suitable for performing an NMR measurement on the fuel cell;

preparing the fuel cell for the NMR process;

optionally using the fuel cell positioning mechanism to insert the fuelcell into the NMR working region; and

performing an NMR measurement on the fuel cell.

EXAMPLES Example 1: In Situ NMR of Li-Ion Battery

A lithium-ion battery with an incorporated stripline detector wasconstructed. Lithium iron phosphate was used as the cathode material andgraphite as the anode material. Lithium iron phosphate LiFePO₄ (LFP) iscommon cathode material in lithium iron phosphate batteries. It has ahigher power density than the more common lithium cobalt oxide LiCoO₂cathode material and a fairly constant discharge voltage at 3.2 V. Usinga charge/discharge current of 0.1 mA, the battery was cycled at 0.1° C.over the course of 10 hours. During the charge and discharge process,⁷Li NMR was acquired to measure the chemical shift (and thus themolecular environment) of the Li ions in the battery. Representativeresulting spectra are shown in FIG. 4.

During discharge, the ⁷Li resonance appeared with a chemical shift ofδ=+13 ppm with respect to a LiCl standard. During the charging cycle,the resonance shifted to higher field, finally reaching δ=−2 ppm duringfull charge. Upon discharge, the resonance shifted back to the δ=+13 ppmposition. Data were acquired for many cycles, with the shifts beingconsistent and repeatable. The fully charged peak is compared with theinitial and final fully discharged peaks in FIG. 5.

These data show that the stripline battery detector can easilydistinguish between the molecular environments of the lithium ions inthe charged state (Lit embedded in the graphite) and the dischargedstate (Lit incorporated in the cathode). In the case of LiFePO₄ as thecathode material as in the above experiments, the presence ofparamagnetic Fe in the sample causes the Li resonance to broadensignificantly. Nonetheless, the changes in chemical environment arestill easily distinguishable. Using other cathode materials such aslithium cobalt oxide or one of the many spinel cathode materials shouldyield even sharper resonances that can distinguish between even smallerchemical shifts.

We claim:
 1. A fuel cell comprising a stripline detector for in situ NMRinside the fuel cell, comprising metallic cathode and anode supportplates arranged in substantially parallel planes and situated onopposite sides of the stripline detector.
 2. The fuel cell of claim 1,wherein the metallic cathode support plate comprises aluminum.
 3. Thefuel cell of claim 1, wherein the metallic cathode support plate furthercomprises a cathode material deposited on the cathode support plate. 4.The fuel cell of claim 3, wherein the cathode material deposited on thecathode support plate is selected from the group consisting of lithiumiron phosphate (LiFePO₄), lithium cobalt oxide (LiCoO₂), and spinelcathode materials.
 5. The fuel cell of claim 1, wherein the metallicanode support plate comprises copper.
 6. The fuel cell of claim 5,wherein the metallic anode support plate further comprises an anodematerial deposited on the cathode support plate.
 7. The fuel cell ofclaim 6, wherein the anode material deposited on the anode support plateis graphite.
 8. The fuel cell of claim 1, further comprising a firstnonconductive separator situated between the stripline detector and themetallic cathode support plate, and a second nonconductive separatorsituated between the stripline detector and the metallic anode supportplate, wherein the first nonconductive separator electrically isolatesthe stripline detector from the cathode, and the second nonconductiveseparator electrically isolates the stripline detector from the anode.9. The fuel cell of claim 8, wherein the first nonconductive separatorand the second nonconductive separator independently comprise a materialselected from the group consisting of polyethylene, polypropylene, andpolytetrafluoroethylene (PTFE).
 10. The fuel cell of claim 8, whereinthe first nonconductive separator and the second nonconductive separatorare the same.
 11. The fuel cell of claim 8, wherein the firstnonconductive separator and the second nonconductive separator are asingle nonconductive separator.
 12. A method for measuring in situ fuelcell nuclear magnetic resonance (NMR), comprising providing the fuelcell of claim 1; connecting the stripline detector to an NMR circuit;isolating electrode leads of the battery from alternating current NMRcircuitry; and cycling the fuel cell while acquiring NMR data from thefuel cell.